1. Field of the Industrial Application
This invention relates to an air-pressure-operated impulsion mechanism used for a nailing machine or the like, in which an impulsion piston slidably fitted in an impulsion cylinder is driven impulsively by compressed air, so that a nail is hammered with a driver coupled to the impulsion piston.
2. Description of the Prior Art
An air-pressure-operated nailing machine is known in the art in which a piston in a cylinder is driven impulsively by compressed air, so that a fixing metal piece such as a nail is hammered into articles such as walls, plates, etc. The conventional nailing machine has an impulsion mechanism as outlined in the part (a) of FIG. 11. That is, an impulsion cylinder 80 is fixedly mounted in a housing (not shown), and an impulsion piston 81 coupled to a driver 82 is slidably fitted in the impulsion cylinder 80, thus dividing the impulsion cylinder 80 into an upper chamber and a lower chamber. Compressed air is introduced into the impulsion cylinder above the impulsion piston 81; i.e., into the upper chamber, so that the impulsion piston 81 is moved downwardly to cause the driver 82 to hammer the nail into the article.
The compressed air introduced into the upper chamber of the cylinder 80 moves the impulsion piston 81 downwardly in FIG. 11. In response to the movement of the impulsion piston 81, a reaction force is produced which acts on the inner surface of the upper chamber of the substantially closed impulsion cylinder 80 to thereby to move the impulsion cylinder 80 upwardly. This reaction force, while moving the impulsion piston 81 impulsively, moves the housing and a shock-absorbing bumper 83 upwardly which is provided in the impulsion cylinder 80 at the lower end. As a result, the impulsion piston is stopped at a position higher than its original stop position by the bumper 83, which reduces the hammering force of the nailing machine.
In order to minimize the bounce of the nailing machine due to the above-described reaction force, it is necessary for the operator to strongly push the nailing machine against the article. Therefore, it is excessively laborious for the operator to use the nailing machine for a vertical wall or a ceiling or to handle it while standing on the unstable scaffold. Furthermore, the force of pushing the nailing machine against the article is liable to fluctuate, and therefore the amount of bounce of the nailing machine is variable, and the hammering force of the latter is also variable.
In order to eliminate the above-described difficulties due to the reaction force, a non-reaction type nailing machine whose hammering force is stable has been proposed in the art for instance by Japanese Utility Patent Application (OPI) No. 29272/1991 (the term "OPI" as used herein means an "unexamined published application"). The nailing machine is as outlined in the part (b) of FIG. 11. The impulsion mechanism of the nailing machine is designed as follows: An impulsion piston 91 is slidably fitted in an impulsion cylinder 90, which is slidably fitted in a housing 94. A piston stopping bumper 93 is arranged in the housing 94. Compressed air introduced into the impulsion cylinder moves the impulsion piston 91 downwardly, and in response to the downward movement of the impulsion piston a reaction force is produced to move the impulsion cylinder 90 upwardly of the housing 94; that is, the reaction force thus produced, acting on the impulsion cylinder 90, is not transmitted to the housing 94.
Hence, the position of the piston stopping bumper 93 is not changed with respect to the article; that is, the impulsion piston stop position is constant at all times, and accordingly the hammering force is consistently maintained. On the other hand, an energizing force, which is provided by the compressed air and by a compression spring 95 for returning the movable impulsion cylinder 90 to the initial bottom dead center, is formed between the impulsion cylinder 90 and the housing 94. Therefore, the movement of the movable impulsion cylinder 90 due to the reaction is transmitted to the housing 94 through the above-described energizing means such as the compression spring 95. Thus, the housing 94 is not completely free from the reaction. In order to eliminate this difficulty, another technique has been proposed in the art. In the technique, the above-described impulsion mechanism is improved as follows: The impulsion cylinder is energized downwardly by using air pressure, and in synchronization with the driving of the impulsion piston, the energizing compressed air is discharged into the outside air, so that the housing is completely free from the reaction. However, the technique is still disadvantageous in that the impulsion mechanism is intricate in arrangement and accordingly the nailing machine is high in manufacturing cost.
On the other hand, an impulsion tool such as a nailing machine is used under various work conditions. For instance in the case where a cover material is nailed to a backing material with a nailing machine, the cover material may be deformed, thus forming a space between the two materials. In this case, it is essential to hold the two materials in close contact with each other by pushing the nailing machine against the surface of the cover material. Even in a nailing operation with the above-described conventional non-reaction type nailing machine, it is necessary to push the nailing machine against the article. When, in order to perform a nailing operation, the operator must stand on the unstable scaffold, the nailing operation is laborious and dangerous.